It is well-known in the art to extend polymers such as polyurethanes. The extended material will then be designated for use in a desired area of utility. Typical of such extending agents is mineral oil, such mineral oil extended polyurethanes being disclosed in U.S. Pat. Nos. 3,714,110 and 3,747,037.
It has also been determined that the mineral oil extended polyurethane is useful in the reclamation and protection of insulated electrical devices. Such a device may, for example, be underground telephone cables which are exposed to fluid contaminants. These contaminants can seriously impair the electrical and mechanical properties of the device. The protectant material is pumped into the cable to remove water that has penetrated into interior free spaces. The material is pumped at low viscosity to achieve an appropriate distribution and then cures in place to a high viscosity. The cured material acts as a hydrophobic barrier to subsequent water penetration. In another application, this material may be utilized as an encapsulant for sealing sections of cable. In this manner, the material serves to prevent, from the outset, the penetration of fluid contaminants.
A mineral oil extended polyurethane useful for this purpose is disclosed in U.S. Pat. No. RE 30,321. That patent defines a cured, cross-linked, mineral oil extended polyurethane prepared from specific polyurethanes and coupling agents, the latter being necessary to compatibilize the mineral oil with the cross-linking urethane elastomer.
Disadvantages of these mineral oil extended polyurethane systems were, however, discovered and described in U.S. Pat. No. 4,168,258. There it was stated that with the earlier mineral oil extended polyurethanes, the mineral oil would tend to migrate toward any grease present in the cable or device to be reclaimed or encapsulated. This grease is encountered more frequently in newer insulated electrical devices. The migration was indicated as causing the formation of an oily film at the grease interface which tended to decrease the reclamation and encapsulant effectiveness of the polyurethane. In order to avoid these difficulties, that patent specifically defined a polyurethane-mineral oil-coupling agent formulation relying on the presence of a polydiene moiety in the polyurethane structure. Mineral oil remained as the extending agent, with the stated preference for including some aromatic carbon content therein.
It is also known that previous polyurethane compositions have been difficult to re-enter after they have fully cured due to their high cast strength and opaque or cloudy color. The high cast strength of these prior art polyurethanes contributes to the difficulty of cutting through or removing cured material from a repaired area, and the opaque color makes it difficult for the operator to establish the exact location to reenter a repair. The ability of these polyurethanes to be easily reentered is important in the repair or encapsulation of insulated electrical or telephone cables when a second splice or connection must be made in the same area as the previous repair or encapsulation. There are also situations where the initial repair or encapsulation is improperly made and has to be re-done.
A vegetable oil extended polyurethane which satisfied these requirements and resolved the reenterability problem is disclosed in U.S. Pat. No. 4,375,521. There, vegetable oil extended polyurethanes comprising a specified polyurethane, a vegetable oil, and a specified plasticizer agent were disclosed for use in reclamation and encapsulation applications. However, these vegetable oil extended formulations tend to cause cracking or stressing of the polycarbonate connectors which are usually present in the cable unit being encapsulated or repaired.
In U.S. Pat. No. 4,355,130, a polyalphaolefin extended polyurethane is disclosed which resolves the stress cracking problem. Such polyalphaolefin extended polyurethanes comprise a specified polyurethane, a specified polyalphaolefin, and, for reclamation and encapsulation purposes, a specified ester coupling agent. The coupling agent is required so that there will be no "spewing" of extender from the cured material.
The use of a coupling agent, however, carries a significant disadvantage. The insulating properties of these prior art polyurethanes are limited due to the presence of ester or other polar groups within the polyurethane structure. When these polyurethanes are used for repair or encapsulation of electrical devices, they are unable to restore the same electrical characteristics because of their higher dissipation factors. This, in turn, results in higher line losses and reduced transmission efficiencies.